JP6881735B2 - Nickel / titanium alloy having a surface layer substantially free of nickel and its manufacturing method - Google Patents

Description

The present invention relates to a nickel / titanium alloy having a surface layer substantially free of nickel and a method for producing the same.

Nickel / titanium alloys (hereinafter referred to as Ni—Ti alloys) are typical shape memory alloys. Shape memory alloys generally have the property of recovering to their original shape even if they are deformed at a temperature above a certain temperature (transformation point), and the original shape when the temperature is above the transformation point even if they are deformed at a temperature below the transformation point. It has the property of recovering to its shape. Ni-Ti alloy has excellent properties such as corrosion resistance, number of uses, durability, and super elasticity among shape memory alloys. Therefore, it is used as an antenna material for mobile phones, wire for body suits, watch bands, and glasses. It is applied in various fields including living tools such as frames, and medical devices such as orthodontic wires, stents, and implants.

In the application of the Ni—Ti alloy to things that are expected to come into contact with the human body, such as living tools and medical devices, the generation of irritation due to the elution of nickel (Ni) contained in the alloy can be a problem. Ni has the property of exhibiting cytotoxicity and inducing allergies, and problems such as skin irritation or allergy caused by Ni have been reported for some time.

Compared to Ni, Ti and its oxide, titanium dioxide (TIO ₂ ), are known to exhibit excellent biocompatibility. Therefore, as an attempt to suppress defects due to the elution of Ni from the Ni-Ti alloy, the Ni-Ti alloy surface layer, that is, the Ni content from the Ni-Ti alloy surface to a certain depth, such as the Ni atomic concentration (Ni) Attempts have been made to lower the atomic concept.

Utilizing the fact that Ti has a higher reactivity with oxygen than Ni, a method has been reported in which a Ni-Ti alloy is thermally oxidized in an oxygen atmosphere to form a surface layer of titanium dioxide on the Ni-Ti alloy. (For example, Non-Patent Document 1). However, the Ni-Ti alloy was originally produced by a method that included multiple heat treatments, such as arc melting Ti and Ni in a vacuum, hot working the resulting ingot, and then repeating annealing and cold working. Since it is manufactured, further heat treatment of the once-manufactured Ni-Ti alloy, thereby pushing oxygen into the alloy, induces structural or structural changes inside the alloy and is superelastic. There is a risk of impairing desirable properties such as.

Further, in the thermal oxidation treatment, a layer having a locally high Ni atomic density tends to be formed at a shallow position on the surface layer of the Ni—Ti alloy. Ni—Ti alloys with such layers can still cause defects due to Ni elution.

Further, by anodizing pure Ti, _{a surface layer of TiO 2} can be formed on the surface thereof, whereby various colors can be imparted to the surface of Ti according to the thickness of the surface layer of _{TiO 2.} It is widely known. Such a color imparts decorativeness to Ti as a metal material, and enhances the utility value of Ti in various applications, particularly applications in daily necessities. However, an alloy of metal and Ti hard anodization, for typically Ni-Ti alloy, or not the surface layer of TiO ₂ is formed be subjected to anodic oxidation, the depth and the surface layer of TiO ₂ formed It was difficult to give a highly decorative color, such as uneven locations.

S. Shabalovskaya, J. Mol. Anderegg, F. et al. Labs, P. et al. Thiel, G.M. Rondoli, J. et al. Biomed. Mater. Res. , 2003, 65B, 193.

An object of the present invention is to provide a Ni—Ti alloy having a surface layer substantially free of Ni and which is less likely to cause problems due to elution of Ni, and a method for producing the same.

The present inventors have found that by anodizing a Ni—Ti alloy in nitric acid at a specific concentration, a Ni—Ti alloy having a surface layer substantially free of Ni can be produced, and the following inventions have been made. Was completed.

(1) A method for producing a Ni-Ti alloy having a surface layer having a nickel atomic density of 10% or less, which comprises a step of anodizing the Ni—Ti alloy in an aqueous solution containing 0.03M to 0.3M nitric acid or nitrate. ..
(2) The production method according to (1), wherein the depth of the surface layer is at least 50 nm from the surface of the Ni—Ti alloy.
(3) The production method according to (1), wherein the anodization is carried out in an aqueous solution of nitric acid or nitrate of 0.05 M to 0.1 M.
(4) The production method according to (3), wherein the depth of the surface layer is at least 100 nm from the surface of the Ni—Ti alloy.
(5) The production method according to (1), wherein the anodization is carried out in an aqueous solution containing 0.1 M nitric acid or nitrate.
(6) The production method according to (5), wherein the surface layer has a nickel atomic density of 5% or less and a depth of at least 100 nm from the surface of the Ni—Ti alloy.
(7) The item according to any one of (1) to (6), further comprising a step of immersing the Ni—Ti alloy in 0.3M to 5M nitric acid for 1 to 48 hours prior to the step of anodizing. Production method.
(8) A Ni-Ti alloy having a surface layer having a nickel atomic density of 10% or less at a depth of at least 50 nm from the surface and a surface having an arithmetic mean roughness of 8 nm or less.
(9) The Ni—Ti alloy according to (8), wherein the nickel atom density at a depth of at least 100 nm from the surface is 10% or less.
(10) The Ni—Ti alloy according to (8), wherein the nickel atom density at a depth of at least 100 nm from the surface is 5% or less.

According to the present invention, it is possible to produce a Ni—Ti alloy having a surface layer substantially free of Ni and which is less likely to cause problems due to Ni elution. Such a Ni—Ti alloy can be a metal material that is safer for the human body and the like while maintaining superelasticity. Further, since the Ni-Ti alloy produced by the method of the present invention exhibits a yellow to blue color, it also has decorativeness as a colored Ni-Ti alloy. Further, the anodizing treatment of the present invention can be carried out at a low temperature close to room temperature, and can be produced at a lower energy cost than heat treatment and the like.

The atomic densities of Ni, Ti and oxygen (O) on the surface of the Ni—Ti alloy anodized in nitric acid at 0.001M (panel A), 0.005M (panel B) and 0.01M (panel C). , This is a profile chart when measured using an X-ray photoelectron spectrometer. The atomic densities of Ni, Ti and oxygen (O) on the surface of the Ni—Ti alloy anodized in nitric acid at 0.03M (panel A), 0.05M (panel B) and 0.1M (panel C). , This is a profile chart when measured using an X-ray photoelectron spectrometer. The atomic densities of Ni, Ti and oxygen (O) on the surface of the Ni—Ti alloy anodized in nitric acid at 0.3M (panel A), 0.5M (panel B) and 1.0M (panel C). , This is a profile chart when measured using an X-ray photoelectron spectrometer. It is a graph which shows the relationship between the concentration of nitric acid and the film thickness of the produced Ni—Ti alloy. It is a photograph of the surface of a Ni—Ti alloy anodized in 0.1M (panel A) or 1.0M (panel B) nitric acid observed with an electron microscope. It is a photograph which shows the appearance of the Ni—Ti alloy anodized in nitric acid of 0.001M to 1.0M. It is a photograph which observed the surface of Ni—Ti alloy anodized in 0.1M nitric acid with a scanning probe microscope. Surface layer of Ni-Ti alloy anodized in 0.1 M nitric acid at nitric acid temperatures of 5 ° C (panel A), 20 ° C. (panel B), 40 ° C. (panel C) or 60 ° C. (panel D). It is a profile chart when the atomic densities of Ni, Ti and oxygen (O) in the above were measured using an X-ray photoelectron spectrometer. Surface of Ni-Ti alloy anodized in 0.1 M nitric acid at nitric acid temperatures of 5 ° C (panel A), 20 ° C. (panel B), 40 ° C. (panel C) or 60 ° C. (panel D). Is a photograph observed with an electron microscope. Ni, Ti and Ni on the surface of the Ni—Ti alloy anodized in 0.1 M nitric acid for 1 hour (panel A), 3 hours (panel B), 6 hours (panel C) or 10 hours (panel D). It is a profile chart when the atomic density of oxygen (O) was measured using an X-ray photoelectron spectrometer. Surface of Ni-Ti alloy anodized in 0.1 M nitric acid (Photo A), 1.0 M nitric acid at 60 ° C for 24 hours, 1.0 M nitric acid at 60 ° C for 3 hours, 1.0 M Each surface of the Ni—Ti alloy anodized in 0.1 M nitric acid after being immersed in nitric acid at 25 ° C. for 24 hours or in 13.14 M nitric acid at 60 ° C. for 24 hours (photos B, C, D, E in that order). ) Is a photograph observed with an electron microscope. Ni-Ti alloy (A) anodized in 0.1M nitric acid and Ni-Ti alloy (B) anodized in 0.1M nitric acid after being immersed in 1.0M nitric acid at 60 ° C. for 24 hours. ), It is a profile chart when the atomic densities of Ni, Ti and oxygen (O) in each surface layer were measured using an X-ray photoelectron spectrometer.

A first aspect of the present invention comprises a surface layer having a Ni atomic density of 10% or less, comprising the step of anodizing the Ni—Ti alloy in an aqueous solution of 0.03M to 0.3M nitric acid or nitrate. The present invention relates to a method for producing a Ni—Ti alloy. The Ni—Ti alloy produced in this embodiment has a surface layer with a nickel atomic density of 10% or less at a depth of at least 50 nm from the surface.

A second aspect of the present invention comprises a surface layer having a Ni atomic concentration of 10% or less, comprising the step of anodizing the Ni—Ti alloy in an aqueous solution of 0.05M to 0.1M nitric acid or nitrate. This is a method for producing a Ni—Ti alloy. The Ni—Ti alloy produced in this embodiment has a surface layer at least 100 nm from the surface and having a nickel atomic density of 10% or less.

A third aspect of the present invention comprises a step of anodizing a Ni—Ti alloy in a 0.1 M nitric acid or nitrate aqueous solution, the Ni—Ti alloy having a surface layer with a Ni atomic concentration of 5% or less. It is a manufacturing method of. The Ni—Ti alloy produced in this embodiment has a surface layer at least 100 nm from the surface and having a nickel atomic density of 5% or less.

The present invention includes the step of anodizing a Ni—Ti alloy in an aqueous solution of nitric acid or nitrate. Since nitrate ions show a dissolving power for Ni due to their strong oxidizing property, it is presumed that Ni can be eluted from the surface layer of the Ni—Ti alloy by anodizing in an aqueous solution containing nitric acid or nitrate. To. As the nitrate, it is preferable to use a salt of a sodium metal such as Na or K and nitric acid, or ammonium nitrate, and particularly preferably ammonium nitrate. The solvent for nitric acid or nitrate may be any solvent that produces nitrate ions when nitric acid or nitrate is dissolved, and is preferably a water-containing solvent, particularly preferably water.

In the present invention, the concentration of nitric acid or nitrate-containing aqueous solution affects the Ni atomic density in the surface layer of the Ni—Ti alloy after anodizing. In the present invention, it is required to anodize the Ni—Ti alloy in an aqueous solution of 0.03M to 0.3M, preferably 0.05M to 0.1M, more preferably 0.1M nitric acid or nitrate. .. In particular, it is preferable to use nitric acid at each of the above concentrations. The molar concentration of nitrate in the present invention is the molar concentration converted to nitrate ion.

For example, Ni—Ti alloy with Ni: Ti = 55: 45 (element number ratio) is anodized in 0.3 M nitric acid to give the Ni atom concentration in the surface layer to a depth of about 60 nm from the surface. Can be 10% or less. Further, by performing anodizing in 0.1 M nitric acid, the Ni atom concentration in the surface layer at a depth of about 125 nm from the surface can be reduced to 10% or less. In the latter, the Ni atom concentration of the surface layer at a depth of about 110 nm from the metal surface is 5% or less.

Further, by performing anodizing in 0.03 M nitric acid, the Ni atom concentration in the surface layer at a depth of about 60 nm from the surface can be reduced to 10% or less, and anodizing is performed in 0.05 M nitric acid. By doing so, the Ni atom concentration in the surface layer at a depth of about 110 nm from the surface can be set to 10% or less. In the latter, the Ni atom concentration of the surface layer at a depth of about 90 nm from the surface is 5% or less.

On the other hand, both the anodizing in 0.01 M nitric acid and the anodizing in 0.5 M nitric acid give the result that the Ni atom concentration of the surface layer from the surface to the depth of 36 nm exceeds 10%. A Ni—Ti alloy having a surface layer with a Ni atomic density of significantly over 10% makes it difficult to suppress the elution of Ni from the surface layer, which may cause problems due to the elution of Ni.

The atomic density of Ni in the surface layer can be measured by using, for example, an X-ray photoelectron spectrometer or the like. Specifically, the Ni—Ti alloy can be subjected to X-ray photoelectron spectroscopy analysis, and the atomic density can be measured from the area of the peak corresponding to the obtained Ni.

The present invention can target Ni—Ti alloys, especially Ni—Ti alloys used as shape memory alloys with superelasticity. Examples include Nitinol NAS Remember Roy (Daiichi Kinzoku Co., Ltd.) and KMS-SM Alloy (Nippon Steel & Sumitomo Metal Corporation).

In the present invention, the Ni—Ti alloy is preferably pre-processed into a desired shape suitable for the mode of use. Such a shape is not particularly limited, and may be a plate shape, a rod shape, a columnar shape, a net shape, a fibrous shape, a porous shape, a sponge shape, a molded product obtained by compressing powder or fibers, a lump, or the like. Good.

The Ni—Ti alloy that can be used in the present invention may contain metal elements other than Ni and Ti as long as it does not impair various properties such as superelasticity. Examples of such metal elements include Group 5 elements such as V, Nb and Ta, Group 6 elements such as Cr, Mo and W, Group 7 elements such as Mn and Re, Fe or Co iron elements, and Ru. , Rh, Pd, Os, Ir, Pt and other platinum group elements, Cu, Ag, Au and other Group 11 elements (1B group elements), Si, Sn, Pb and other Group 14 elements (4B group elements), Y, Group 3 elements such as La, Ce, Nd, Sm, Tb, Er, Yb, and Ac can be mentioned.

The anodizing in the present invention is preferably carried out by adjusting the temperature in the range of 10 ° C. to 20 ° C. by using an appropriate cooling means in addition to adjusting the concentration of nitric acid or nitrate. If anodizing is continued in a state where the temperature exceeds 40 ° C., the surface of the produced Ni—Ti alloy tends to be rough.

The anodization in the present invention is preferably performed in a constant current mode, in which case the voltage is automatically determined from the relationship between the current and the electrical conductivity of the solution.

The current density of anodizing in the present invention may be 10 mA / cm ² or more, preferably 25 mA / cm ² or more, and more preferably 50 mA / cm ² or more.

Further, the anodizing under the above conditions may be carried out in the range of 30 minutes to 20 hours, preferably 1 hour to 10 hours, and more preferably 1 hour to 6 hours.

Anodization can be performed at room temperature by applying direct current, AC / DC superimposition, or pulse waves. Alternatively, it is also possible to apply a single-phase half-wave, a three-phase half-wave, or a six-phase half-wave by using a DC power supply based on a thyristor method.

In a typical embodiment, a Ni-Ti alloy and platinum are immersed in a suitable bath filled with 0.1 M nitric acid as an anode and a cathode, respectively, and power is supplied by a DC power supply device to obtain a current density of about 10 to 100 mA /. Anodize at about ^{cm 2.} This makes it possible to produce a Ni—Ti alloy having a Ni atom concentration on the surface layer at a depth of about 125 nm of 10% or less, and particularly a Ni atom concentration on the surface layer at a depth of about 110 nm of 5% or less.

The anodized Ni—Ti alloy may be washed after being removed from the nitric acid or nitrate aqueous solution. Washing can be performed with water or an organic solvent such as methanol, ethanol or acetone.

In any of the above embodiments, the Ni—Ti alloy is mixed with 0.3M to 5M nitric acid, preferably 0.5M to 3M nitric acid, preferably 3 to 48 hours prior to the anodizing step. It is preferable to further include the step of immersing for 24 hours. By anodizing the Ni—Ti alloy under the above conditions after such immersion, it is possible to produce a Ni—Ti alloy with a smoother metal surface, better durability and more suppressed Ni elution. it can. The temperature of immersion may be room temperature, or may be appropriately heated.

The anodizing of the Ti—Ni alloy in the present invention can reduce the atomic concentration of Ni in the surface layer of the alloy and at the same time form the surface layer of titanium dioxide, resulting in a yellow to blue surface of the Ni—Ti alloy. Can be colored. The color depends on the depth of the titanium dioxide surface. From the above, the method according to the present invention is a method for producing a colored Ni—Ti alloy having a surface layer having a nickel atomic density of 10% or less, which includes a step of anodizing the Ni—Ti alloy under the above conditions. It can also be represented.

As a fourth aspect, the present invention has a surface layer having a nickel atomic density of 10% or less at a depth of at least 50 nm from the surface and a surface having an arithmetic mean roughness (Ra) of 8 nm or less, preferably 6 nm or less. A nickel-titanium alloy is provided. A preferred example of this embodiment is a nickel-titanium alloy having a surface layer having a nickel atomic density of 10% or less at a depth of at least 100 nm from the surface and a surface having a Ra of 6 nm or less, and a more preferred example is at least 100 nm from the surface. A nickel-titanium alloy having a surface layer having a nickel atomic density of 5% or less and a surface having a Ra of 6 nm or less. Such a Ni—Ti alloy can typically be produced by the method of the first to third aspects.

Arithmetic mean roughness (Ra) is expressed by extracting the reference length from the roughness curve in the direction of the average line, summing the absolute values of the deviations from the average line of the extracted part to the measurement curve, and averaging them. It is a commonly used unit that expresses the surface roughness to be obtained. The surface roughness of a Ni—Ti alloy having a titanium dioxide surface layer is related to the durability of the titanium dioxide surface layer, and if the surface is rough, the durability tends to be inferior. The surface of the Ni—Ti alloy of the present invention has a low Ra value of 8 nm or less, and it is presumed that the surface layer of titanium dioxide of such an alloy has high durability.

The Ni-Ti alloy obtained by the method of the present invention is widely used as a metal material that is less likely to cause defects due to elution of Ni and as a highly decorative metal material that is colored while maintaining the characteristics related to shape memory. Available in the field. For example, it can be used for body suit wires, watch bands, eyeglass frames and other living utensils, orthodontic wires, stents, implants and other medical utensils, general building materials, cooking utensils, tableware, sanitary ware, etc. is there.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present examples are provided merely for the purpose of explaining the present invention and for reference in specific embodiments thereof, and the scope of the invention. Does not limit or limit. In addition, all the examples can be carried out or carried out by those skilled in the art using standard techniques or methods, except as described in detail.

<Example 1>
1) Production example Prepare a bath filled with 200 mL of a nitric acid aqueous solution of 0.001M, 0.005M, 0.01M, 0.03M, 0.05M, 0.1M, 0.3M, 0.5M or 1.0M, respectively. Then, a plate of Ni—Ti alloy (diameter 17 mm × thickness 3 mm) of Ni: Ti = 55: 45 (element number ratio) was used as an anode, and a Pt plate of the same size was used as a cathode and immersed in each bath, and the current density was 50 mA. Anodizing was carried out for 180 minutes under the conditions of / cm ² and the temperature of the nitric acid aqueous solution in the bath at 20 ° C. to produce a Ni—Ti alloy. Anodizing treatments in 0.03M, 0.05M, 0.1M and 0.3M aqueous nitric acid solutions are examples of 0.001M, 0.005M, 0.01M, 0.5M and 1.0M aqueous nitric acid solutions. The anodizing treatment inside corresponds to each of the comparative examples.

2) Test example 2) -1. Measurement of Ni Atomic Density The Ni—Ti alloy produced in 1) above was profile-analyzed with an X-ray photoelectron spectrometer (PHI5000 VersaProbe, ULVACPHI Co., Ltd.) to determine the atomic densities of Ni, Ti and O (oxygen). It was measured. Profile charts of each Ni—Ti alloy are shown in FIGS. 1-3. Further, FIG. 4 shows a graph in which the vertical axis is the depth (film thickness) at which the atomic density of oxygen on the metal surface is halved and the horizontal axis is the concentration of the aqueous nitric acid solution.

As shown in FIGS. 1-3, in the Ni—Ti alloy corresponding to the examples, the Ni atomic density is less than 10% even at a depth from the metal surface of 50 nm, while the Ni—Ti alloy corresponding to the comparative example. The alloy had a depth from the metal surface of 10 to 30 nm and a Ni atomic density of more than 10%. Further, as shown in FIG. 4, the film thickness was maximized by anodizing in a 0.1 M aqueous nitric acid solution.

2) -2. Electron Microscope Observation Using a scanning electron microscope (JCM-5000 Neo Alloy) manufactured by Nippon Denshi Co., Ltd., Ni was anodized in a 0.1 M or 1.0 M nitrate aqueous solution in 1) above according to the manufacturer's manual. The surface of the −Ti alloy (Comparative Example, Example) was observed. The electron micrograph is shown in FIG.

It was confirmed that the surface of the alloy anodized in a 1 M aqueous nitric acid solution had a large number of rough irregularities as compared with that of the alloy anodized in a 0.1 M aqueous nitric acid solution. Since such surface roughness causes a decrease in the durability of the metal surface or the surface layer of titanium dioxide, the Ni-Ti alloy according to the present invention has higher durability than the Ni-Ti alloy of the comparative example. It was speculated that it was.

2) -3. Appearance Observation Fig. 6 shows the appearance of the Ni—Ti alloy produced in 1) above. Multicoloring of light blue, yellow, purple, green, etc. can be clearly observed from anodizing in a 0.03 M aqueous nitric acid solution, and the bluish color fades when anodized in an aqueous nitric acid solution of 0.5 M or more. It was observed that there was a tendency.

2) -4. Measurement of Surface Roughness The surface of a Ni-Ti alloy that was anodized in a 0.1 M nitric acid aqueous solution in 1) above using a scanning probe microscope (SPM-9700, Shimadzu Corporation) according to the manufacturer's manual. When the roughness was observed and the arithmetic mean roughness was calculated from the image (FIG. 7), a result of 5.6 nm was obtained.

<Example 2>
Anodization was carried out under the same conditions as in Example 1 except that the concentration of the aqueous nitric acid solution was fixed at 0.1 M and the temperature of the aqueous solution was set to 5 ° C., 20 ° C., 40 ° C. or 60 ° C. The anodized Ni-Ti alloy was profile-analyzed with an X-ray photoelectron spectrometer (PHI5000 VersaProbe, ULVACPHI, Inc.) in the same manner as in Example 1, and the atomic densities of Ni, Ti and O (oxygen) were measured. .. The profile chart is shown in FIG. Further, using a scanning electron microscope (JCM-5000 Neo Scoppe) manufactured by Nippon Denshi Co., Ltd., the surface of the anodized Ni-Ti alloy was observed according to the manufacturer's manual. The electron micrograph is shown in FIG.

It was confirmed that when the temperature of the aqueous solution was 40 ° C. or higher, the Ni atom concentration exceeded 10% in the surface layer at a depth of about 36 nm from the surface of the Ni—Ti alloy. On the other hand, it was confirmed that when the temperature of the aqueous solution reached 5 ° C., the surface roughness of the Ni—Ti alloy tended to increase. From these results, it was inferred that the temperature of the aqueous nitric acid solution during anodization should be around 20 ° C.

<Example 3>
Anodization was carried out under the same conditions as in Example 1 except that the concentration of the aqueous nitric acid solution was 0.1 M and the anodizing time was 1 hour, 3 hours, 6 hours or 10 hours. The anodized Ni-Ti alloy was profile-analyzed with an X-ray photoelectron spectrometer (PHI5000 VersaProbe, ULVACPHI, Inc.) in the same manner as in Example 1, and the atomic densities of Ni, Ti and O (oxygen) were measured. .. The profile chart is shown in FIG.

Although the Ni electron density of the surface layer tends to increase slightly after 10 hours of anodizing, it is confirmed that the Ni atom concentration of the surface layer at a depth of about 50 nm from the metal surface is less than 10% at any treatment time. Was done.

<Example 4>
1) Ni: Ti = 55: 45 (element number ratio) Ni-Ti alloy (diameter 17 mm x thickness 3 mm) plate in 1.0 M nitric acid at 60 ° C for 24 hours (B), 1.0 M. The mixture was immersed in nitric acid at 60 ° C. for 3 hours (C), in 1.0 M nitric acid at 25 ° C. for 24 hours (D), and in 13.14 M nitric acid at 60 ° C. for 24 hours (E). Plate after immersion an anode, a cathode and Pt plate of the same size, were immersed in a bath filled with 0.1M nitric acid aqueous solution, under conditions of a current density of 50 mA / cm ^2, and the temperature 20 ° C. aqueous solution of nitric acid in the bath Then, anodic oxidation was performed for 180 minutes.

2) Using a scanning electron microscope (JSM-6701) manufactured by Nihon Denshi Co., Ltd., the surfaces of Ni—Ti alloys (B) to (E) anodized by 1) above were observed according to the manufacturer's manual. .. The electron micrograph is shown in FIG. By immersing in 1.0 M nitric acid before anodizing and then anodizing, the surface roughness is improved as compared to the case where the Ni—Ti alloy was anodized without anodicing (A in FIG. 11). It was confirmed that the Ni-Ti alloy could be obtained. On the other hand, when the Ni—Ti alloy was immersed in 13.14M nitric acid (E), it was confirmed that holes were formed on the surface of the plate after anodization.

3) The Ni-Ti alloy (B) produced in 1) above was profile-analyzed with an X-ray photoelectron spectrometer (PHI5000 VersaProbe, ULVACPHI Co., Ltd.) to determine the atomic densities of Ni, Ti and O (oxygen). It was measured. A profile chart of each Ni—Ti alloy is shown in FIG. It was confirmed that even when the dipping treatment was performed, the depth of the surface layer having the nickel atom density of 10% or less was almost the same as that when the dipping treatment was not performed (A in FIG. 12).

Claims (9)

A method for producing a nickel-titanium alloy having a surface layer of titanium dioxide having a nickel atomic density of 10% or less, which comprises a step of anodizing the nickel-titanium alloy in an aqueous solution of 0.03M to 0.3M nitric acid or nitrate. The production method, wherein the depth of the surface layer is at least 50 nm from the surface of the nickel-titanium alloy. The production method according to claim 1, wherein the anodization is carried out in an aqueous solution of nitric acid or nitrate of 0.05 M to 0.1 M. The production method according to claim 2, wherein the depth of the surface layer is at least 100 nm from the surface of the nickel-titanium alloy. The production method according to claim 1, wherein the anodization is carried out in an aqueous solution containing 0.1 M nitric acid or nitrate. The production method according to claim 4, wherein the surface layer has a nickel atomic density of 5% or less and a depth of at least 100 nm from the surface of the nickel-titanium alloy. The production method according to any one of claims 1 to 5, further comprising a step of immersing the nickel-titanium alloy in 0.3 M to 5 M nitric acid for 1 to 48 hours before the step of anodizing. A nickel-titanium alloy having a surface layer of titanium dioxide having a nickel atomic density of 10% or less and a surface having an arithmetic mean roughness of 8 nm or less at a depth of at least 50 nm from the surface. The nickel-titanium alloy according to claim 7, wherein the nickel atomic density at a depth of at least 100 nm from the surface is 10% or less. The nickel-titanium alloy according to claim 7, wherein the nickel atomic density at a depth of at least 100 nm from the surface is 5% or less.

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